Cover system with gas collection system for waste sites and environmental closures

ABSTRACT

A cover system is provided for waste sites and environmental closures, in which the cover system comprises a synthetic grass and an impermeable geomembrane that can be applied without the use of heavy earthwork equipment as temporary or final cover to control odors, erosion, gas migration and contaminate migration. The invention allows installation on very steep slopes and does not require the use of an extensive anchoring system to resist wind uplift or slope failure. A gas collection system is located under the cover system for the collection of gas produced by the waste sites.

This application is a continuation-in-part of, and claims the benefitof, U.S. patent application Ser. No. 11/900,831, filed Sep. 13, 2007,which claims the benefit of U.S. Provisional Patent Application Ser. No.60/844,576, filed Sep. 14, 2006.

TECHNICAL FIELD

This invention relates to a cover system for waste disposal sites andother environmental closures. In a more specific aspect, this inventionrelates to a cover system for waste disposal sites and otherenvironmental closures, wherein the cover system comprises syntheticgrass and an impermeable geomembrane. In another more specific aspect,this invention relates to such a cover system which includes a systemfor the collection of gas produced by the waste sites. In further a morespecific aspect, this invention relates to such a cover system whichincludes a drainage system comprising a synthetic drainage component.

In this application, the following terms will be understood to have theindicated definitions:

-   -   waste sites—refers to earthern berms and to sites where waste is        deposited, such as landfills, phosphogypsum stacks,        environmentally impacted land, leach pads, mining spoils and        environmental closures or material stockpiles that require a        closure or cover system.    -   synthetic grass—refers to a composite of at least one geotextile        (woven or nonwoven) tufted or knitted with one or more synthetic        yarns or strands that has the appearance of grass.    -   geomembrane—refers to a conventional or textured polymeric        material, such as high density polyethylene, very low density        polyethylene, linear low density polyethylene, polyvinyl        chloride, etc.

BACKGROUND OF THE INVENTION

The prior art discloses cover systems for the closure of variouslandfill and other sites. However, such covers with an exposed membranegenerally have negative aesthetics. Additionally, the prior artgenerally requires multiple anchors and very closely spaced trenches toresist wind uplift on the exposed membrane. Thus, the industry continuesto search for improved cover systems which are effective, economical andmeet the various local, state and federal environmental laws, rules andguidelines for these systems.

Artificial grass has been extensively used in sport arenas as well asairport runways and general landscaping. A primary consideration ofartificial turf playing fields is the ability of the field to drain.Examples of prior art in synthetic grass drainage are U.S. Pat. Nos.5,876,745; 6,858,272; 6,877,932 and 6,946,181. However, theseapplications are generally only for field playing surfaces where theground is substantially flat and the concern is only with the ability toimprove field playing conditions.

The drainage use in the prior art deals principally with slowinfiltration of flat surfaces to avoid inundation of the field, and suchdrainage use generally cannot handle the very large and rapid run-offthat would occur on very large and steep sideslopes of landfills andmine stockpiles.

In addition, the prior art does not provide a cover system which has anefficient system for the collection of gas produced by the waste sites.

SUMMARY OF THE INVENTION

Briefly described, the present invention provides a new and usefulsystem for covering (i.e., closing) various types of waste sites wherewaste is deposited. More particularly, the cover system of thisinvention comprises (1) a composite of one or more geotextiles which aretufted or knitted with one or more synthetic yarns, and (2) animpermeable geomembrane which is comprised of a polymeric material and(3) a system for the collection of gas produced by the waste sites. Thiscover system optionally includes a synthetic drainage component.

The cover system of the present invention eliminates or at least reducesemissions from the waste and, in addition, either reduces or eliminatesthe infiltration of water into the underlying waste.

This invention relates to combining an impermeable liner with syntheticturf that provides a natural grass like appearance to the final cover.The cover system of this invention generally use a drain liner (such asthat shown in U.S. Pat. No. 5,258,217) to provide drainage of the systemin very steep slopes. The invention also allows for other drainagesystems (such as a high density polyethylene drainage net) to be used ontop of a roughened textured geomembrane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in cross-section of a typical final cover system asdescribed in current EPA Federal Regulations and used in the covers oflandfills and mines.

FIG. 2 is a view in cross-section of a cover system according to thepresent invention, with an encircled portion.

FIG. 2.1 shows the encircled portion of FIG. 2 in enlarged detail.

FIG. 2A is a view in cross section of a cover system according to thepresent invention, with an encircled portion of the cover using analternative drainage geonet directly on top of the geomembrane as adrainage system.

FIG. 2B shows the encircled portion of FIG. 2A in enlarged detail.

FIG. 3 is a view in cross-section of a cover system according to thepresent invention, with an encircled portion showing a corner portion ofthe cover system.

FIG. 3.1 shows the encircled portion of FIG. 3 in enlarged detail.

FIG. 4 is a view in cross-section of a cover system according to thepresent invention on a slope, showing the drainage flow.

FIG. 5 is a view in cross-section of a cover system according to thepresent invention on a slope, showing the critical length of drainage.

FIG. 6 shows the results of transmissivity testing on a cover systemaccording to the present invention.

FIG. 6.1 shows the results of transmissivity testing of FIG. 6 in graphform.

FIG. 7 shows the results of interface friction testing on a cover systemaccording to the present invention.

FIG. 8 is a table showing critical length results for a large rainfallintensity of 4 inch/hr at varying slope angles.

FIG. 9 is a view in cross-section of an alternative anchoring systemaccording to the present invention.

FIG. 9.1 shows the half wrap option of the alternative anchoring systemof FIG. 9.

FIG. 9.2 shows the complete wrap option of the alternative anchoringsystem of FIG. 9.

FIG. 10 shows, in cross section, a cover system according to thisinvention, including an embodiment of the gas collection system.

FIG. 11 is a view of a side slope of a landfill site covered by thecover system of this invention including the details of an embodiment ofthe gas collection system.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a cover or closing system for sites wherevarious types of waste have been deposited. As noted above, these wastesites can include earthern berms, landfills, phosphogypsum stacks, leachpads, mining spoils, soil stockpiles, etc.

In the present invention, a synthetic grass is used in combination withan impermeable geomembrane to provide a new and useful cover system.This combination (sometimes referred to as a composite material) can beused in the slopes and crowns of the waste sites.

The cover system of this invention includes a system for the collectionof gas produced by the waste sites. This gas collection system comprisesone or more strips of geocomposite drainage material connected to one ormore collection pipes which collect and conduct the gas to one or moreheader pipes. The header pipe(s) may be connected to a blower to removethe gas from the waste site. This gas collection system is located underthe cover system.

The cover system of this invention represents an innovative and economicapproach to hazardous and solid waste landfills and other environmentalclosures. These facilities are typically required to be closed with afinal cover consisting of layers of soils and geosynthetic materials.The purposes of the cover system of this invention are to preventexposure of the waste to the environment, to enhance collection oflandfill gas and to minimize infiltration of storm water which resultsin leachate in the landfill.

With the cover system of this invention, owners and operators canrealize significant cost savings by constructing a cover system withsynthetic grass that does not require the vegetative support and topsoillayer of the typical final cover system. The synthetic grass/impermeablelayer of this invention is particularly applicable to sites where thedesign life of the cover system is short (for example, less than 10years) or long (for example, more than 10 years); when future removal ofthe cover may be required (e.g., for landfill reclamation); when thelandfill slopes are too steep to allow for the placement of soil on topof the liner; when cover soil is not readily available; when thelandfill may be expanded vertically at a later date; or simply to allowthe construction of rapid closures to control emissions and odors.

The cover system of this invention is preferably designed with (1) alower impermeable layer placed over the soil intermediate covercomprising a drain liner geomembrane (or textured geomembrane liner) anda geonet drainage media, or alternatively a drain liner with studsincorporated in the high density polyethylene sheet that acts asdrainage; (2) a synthetic grass that is engineered with polyethylenefibers with a length of at least about 1.0 to about 2.5 inches tuftedinto two fabrics comprising either needle punch non-woven polyethyleneor woven polypropylene geotextiles; and (3) a sand layer of about 0.5 toabout 1.5 inches that is placed as infill to ballast the material andprotect the system against wind uplift. The sand will provide additionalprotection of the geotextiles against ultraviolet light.

The synthetic grass technology was originally developed primarily forprofessional sport venues. The polyethylene yarns durability against UVlight lends itself well to the closure cover on environmental projects.On landfills and mine piles, sliding of the cover along steep sideslopesis of primary concern, particularly after major storm events. Thepresent invention is designed to resist sliding failure through frictionand drainage elements incorporated into the cover system. The permeableturf percolates at different rates, such as approximately a rate of 180gallons/sq ft/hr (0.2 cm/sec) or faster. During a rain event, therainfall will penetrate quickly through the sand infill and draindirectly in the geocomposite drainage system below to minimize erosionand maintain stability of the sand infill. The infill is also held inplace by the synthetic grass that traps the sand to anchor and ballastthe synthetic grass turf to the surface it covers.

If concerns associated with long-term survivability of the productprevent regulatory approval for final exit closure (i.e. no furtherregulatory actions required to achieve an approved final closure), theproposed synthetic grass could then be simply covered with 2 feet ofsoil.

The materials of this invention have been tested under this scenario(200 lbs/sq.ft) using ASTM transmissivity testing. The system willperform as in the conventional U.S. EPA Subtitle “D” caps since thegeocomposite drainage media used for drainage above the geomembrane toimprove stability already exists. Refer to FIG. 1.

With this invention, however, an anchoring system typically associatedwith exposed geomembrane covers will not be required. The turf isballasted with approximately about 0.5 to about 1.5 inch of sand infill,which produces a weight of about 6 to about 12 pounds per square foot.The infill is held in place by the artificial blade polyethylene fibertufted to the lower geotextiles. This geometry traps the sand to anchorand ballast the turf product to the surface covered by the syntheticgrass.

The selection of the chemical composition of the syntheticgrass/impermeable membrane is a critical element of the presentinvention. The polymer should resist exposure to sunlight, whichgenerates heat and contains ultraviolet radiation. The polymer yarnsshould not become brittle when subjected to low temperatures. Theselection of the synthetic grass color and texture should beaesthetically pleasing.

The actual grass like component preferably will consist of polyethylenefibers of about 1.5 to about 2.5 inches in length tufted into a blackwoven and/or a gray non-woven geotextile. For added strength in severelysteep sideslopes, an additional mesh backing can be tufted for improvingdimensional stability. The polyethylene grass filaments preferably havean extended operational life of at least about 40 to about 50 years.

This invention combines the use of a synthetic grass on final landfillcovers to provide a pleasant visual appearance and provides a drainagesystem that can handle the very rapid run-off. Thus, the cover system ofthis invention can be installed on very steep slopes which typicallyoccur in landfills and stockpiles. This invention also provides foranchoring to resist significant uplift forces caused by high wind loads.

There are many advantages to the cover system of this invention, suchas:

-   -   There is an absence of soil cover, which will reduce        construction costs depending on the availability of soil at the        site.    -   Reduces annual operation and maintenance requirement while        providing superior and reliable/consistent aesthetics.    -   Reduces the post closure maintenance costs of the cover.    -   Reduces the need for expensive riprap channels and drainage        benches, with substantially no erosion or siltation problems,        even during severe weather.    -   Better for landfills in sensitive areas where soil erosion and        sedimentation are major concerns because soil loss is        substantially reduced during operations and post-closure.        Eliminates the need for additional borrow sources, siltation        ponds and associated environmental construction impacts.    -   Allows for steeper waste pile slopes, because there will be a        reduced risk of soil stability problems, such as resulting from        earthquakes or gas pressure build-up.    -   Reduces infiltration through the cap. Surface water is rapidly        drained off and is not restricted by the hydraulic conductivity        of the cover system. As a result, the hydraulic head on the        impermeable layer and subsequent infiltration into the waste is        minimized. HELP (Hydraulic Evaluation of Landfill Performance)        infiltration models show that this type of cover will have less        infiltration than current covers allowed by federal regulations.    -   Enhanced visual inspection. Because the synthetic materials are        exposed, the cover system of this invention is easily inspected        for damage which, if identified, may be easily and inexpensively        repaired. Also the majority of damage to the synthetics caps is        produced by the earthwork equipment during soil placement. By        eliminating the soil layer with this cover system, this is no        longer an issue.    -   Allows faster capping and installation during the operational        life of the landfill and during wintertime. Faster capping        reduces odors, improves gas collection efficiency and enhances        compliance with federal air quality regulations.    -   Easier access to landfill materials for reclamation in the event        of future landfill reclamation for future piggyback areas or        future waste lifts due to waste settlement or vertical        expansion. The composite material of this invention allows the        owners access to the waste without having to remove the existing        cover soils of a typical and traditional final cover system.    -   Reduces wildlife impacts on the cover because there is no food        or organic matter. This is important in landfills located in        coastal areas or those facilities located near airports.

An alternative closure (i.e., a cover system according to the presentinvention and intended for use for a period of less than about 40-50years) can be used under the following conditions:

-   -   On areas that will be overfilled or mined in the future.    -   To limit landfill leachate generation before final closure        occurs.    -   To allow the waste subgrade to gain strength and allow for        additional waste placement in the future.    -   As a means to control landfill gas or odors by enhancing        collection capabilities.    -   As a partial final cover and delay future capital associated        with the soil cover.    -   Reduce operational costs for grass cutting and erosion control        during the operative life of the facility.    -   As part of an agreement/consent order to control emissions and        minimize odors to surrounding communities and to reduce fines        and notices of violation due to soil erosion issues.    -   To control dust air emissions due to high winds on landfills or        stockpiles, particularly in areas where vegetation will not        grow.

Use of this system for more than 40-50 years may involve periodicreplacement or UV treatment of the synthetic grass component of thesystem.

Gas Collection System

Landfill gas is a product of bacterial decomposition of organic matterdeposited in a waste site or landfill, combined with either integratedmoisture within the waste or moisture invading the waste. Landfill gasproduction will generally continue until all the organic matter in thewaste is decomposed.

The gas collection system of this invention serves as an active orpassive gas collection system and provides significant improvements tothe current methods of control and collection of landfill gas. Examplesof such improvements include:

-   -   A faster closure, which allows for a more efficient containment        of landfill gas.    -   Less methane emissions from the surface area of the landfill        cover system.    -   Less susceptible to failures or soil slides caused by a positive        pressure buildup under the cover system.    -   Significantly greater capture and containment of landfill gas by        combining the cover system with a composite drainage system        under the cover system.    -   Easy conversion from a temporary passive system to an active        system.    -   Eliminates or minimizes vertical gas collection wells which are        costly and difficult to maintain their integrity.

The gas collection system is located under the bottom impermeable layerof the cover system, where landfill gas is controlled or diverted viabarriers and gas conduction systems. As shown in FIGS. 10-11, the systemcan operate under passive collection conditions or under negativepressure (active conditions) to collect the gas for distribution to aflare and/or beneficial reuse.

The gas collection system of this invention preferably uses a highlypermeable and transmissive synthetic media system for collection andtransmission of landfill gas. Sections of the synthetic media system arepreferably spaced at about 30 to about 50 feet intervals along theslopes of the landfill. Alternatively, one section of the syntheticmedia system can cover the entire area of the landfill. The syntheticmedia system allows the gas flow for passive venting and collection. Thegas can also be directed under negative pressure to flow towardsdesignated areas, such as to a flare and/or beneficial reuse.

The gas collection system preferably includes the cover system and thesynthetic media system located under the cover system. Alternatively,venting systems comprising underground articulated piping (such aspolyethylene or polyvinyl chloride) embedded in gravel under the coversystem collect and conduct the gas by natural gas pressure to verticalventing stand pipes located away from the landfill. The articulatedpiping allows the pipes to flex with the compacting, decomposing waste,to avoid breakage and potential for gas leaks. Gravel in the trenchesmay further allow gas to escape controllably either by induced vacuum ornatural gas pressures.

The synthetic media system terminates outside the closure area by meanssuch as wrapping around a perforated pipe section. These pipe sectionsare connected to a non-perforated pipe section which, in turn, isconnected to a header or lateral pipe which leads to the active orpassive gas extraction system. Other means may involve connecting thesynthetic media system directly to the header or lateral pipe.

Referring now to the drawings, in which like numbers represent likeelements, FIG. 1 shows a cover system according to the prior art with anintermediate soil cover 101.

As shown by the embodiment of FIG. 2, the present invention provides acover system 100 for draining pre-engineered synthetic turf 103/104 ontop of a geomembrane 102 having studs that when covered by the bottomgeotextile 104 of the turf creates a highly transmissive drainage. Thesynthetic turf will be used as the upper component of a landfillclosure. For example, the turf can be constructed using a knittingmachine that may use over 1,000 needles to produce a turf width of about15 feet. The geomembrane is preferably made of very low densitypolyethylene, linear low density polyethylene (LLDPE), high densitypolyethylene (HDPE), or polyvinyl chloride and contains a series ofstuds (such as the 50-mil LLDPE sold under the trademark Super GripNetby AGRU America, Inc.). The geomembrane 102 is 22.5 feet wide and isdeployed on the surface of the area of the landfill to be closed. Thesynthetic grass also comes in rolls 15 feet wide and is deployeddirectly on top of the geomembrane 102. The system is ballasted withabout 0.5 to about 1.5 inch of clean sand. The geotextiles 104 of thesynthetic grass prevent the sand from entering the interstices/studs ofthe geomembrane 102 or the high density polyethylene drainage net 106(as shown in FIG. 2A).

The resulting composite cover has a high transmissivity value exceeding3.5×10⁻³ sq.meters/sec. See FIG. 6 for actual test results.(Alternatively, in other applications the transmissivity value may notbe as high.) The drainage is very important because rain on the closuresurface penetrates quickly through the sand and geotextiles into thelower impermeable geomembrane and is directed to a series of drainagetrenches or surface benches to the site perimeter ditches and ponds (notshown).

This invention can be used as cover on very steep slopes (i.e., 3horizontal:1 vertical) in landfills and other environmental applicationswith large man made stockpiles. To prevent the movement of the sandinfill 105, it is necessary to ensure the surface water run offpermeates through the sand and synthetic grass layers into the spacesbetween the studs of drain liner. The geomembrane 102 in this inventioncan transmit the water up to a certain distance (i.e., critical length)before the drainage system is flooded and run-off would start eroding orwashing the sand down the slope. FIG. 5 shows the critical flow lengthon a slope application.

For the cover system of this invention, the critical length fordifferent rainfall intensities can be calculated by the followingequation:

q·t≧R·t L·cos α

where:

-   -   q=flow rate of the drain liner at I=sin α;    -   t=duration;    -   α=angle of land fill cover slope as defined in FIGS. 4 and 5    -   R=rainfall intensity (ft/hour); and    -   L=arbitrary length measured from the slope crest (FIG. 5)

The critical drainage slope length is defined as:

$L_{CR} = \frac{q}{{R \cdot \cos}\; \alpha}$

Based on the transmissivity test results (refer to FIG. 6), L_(CR) iscalculated using a rainfall intensity R=4 in/hour (0.333 ft/hour) andshown in FIG. 8. With the above equation the drainage length of thesystem can be calculated depending on the design rain event. The systemwill then need to be drained to the typical surface water benches ortrenches to the site surface water ponds. If the critical drain slopelength is not of sufficient distance, then the sand could be placed instrips at designated locations only providing the anchoring requirementsand avoiding the sand movement caused by saturating the drainage systemand percolating of water into the sand. Anchoring can also be usedthrough the application of a synthetic grass wrap 107 created byencasing loose sand or sandbags 108 in a synthetic grass panel anddeploying parallel to the slope or with the slope. Based on the exitclosure requirements, a drainage system may or may not be requiredexcept underneath the synthetic grass anchor to allow for pass-throughwater and water force dissipation. Refer to FIG. 9.

The seepage parallel to slope within the sand layer is calculated asfollows: As shown in FIG. 5, seepage parallel to the slope within thesand layer can occur when the actual slope length is longer than L_(CR).In this case (flow conditions over the slope length L_(S2)), the flowlines are parallel to the slope surface and the seepage force J actingon the soil volume of L_(CR)×h×1 is equal to:

J=V·γ _(w) sin α

Assuming the artificial grass interface has an effective frictionangle=δ′ and no adhesion, then the following force equilibrium equationis established,

Vγ _(b) cos α tan δ′=V·γ _(w) sin α+V·γ _(b) sin α

This equation can be rearranged as:

${{Tan}\; \alpha} = {\frac{\gamma_{b}}{\gamma_{b} + \gamma_{w}}\tan \; \delta^{\prime}}$

where:

-   -   α=slope angle;    -   γ_(b)=buoyant soil unit weight;    -   γ_(w)=water unit weight; and    -   δ′=effective friction angle of the interface between the        sand-artificial grass layer        It is noted that γ_(b) is approximately equal to γ_(w) and the        maximum possible stable slope angle is about half of δ′. In        other words, seepage reduces the maximum stable slope angle to        about half of that for no water flowing parallel to the slope        surface. From the above equation the stability of the system can        be evaluated. FIG. 7 shows friction testing of the present        invention. The testing shows a value of internal friction of 43        degrees, thus if the value is reduced by half then the maximum        slope that the material could be placed under rainfall        conditions would be at slope of 21.5 degrees which steeper than        a 3 horizontal:1 vertical slope.

Materials Description

-   -   Linear low density polyethylene, polyvinyl chloride, high        density polyethylene and very low density polyethylene are        preferred materials for the impermeable geomembrane and the        synthetic drainage component of this invention.    -   High density polyethylene drainage net over texture HDPE sheets        (refer to FIG. 2A) or drain liners such as Super GripNet (refer        to FIG. 2). The purpose of this component is to increase the        friction coefficient of the layering system. Thus, if a two feet        of soil cover, as required on top by environmental regulations,        is desired for final exit closure, the friction characteristics        of the system are capable of sustaining the soil cover on steep        slopes.    -   Weather and water resistant colored (such as green) yarns        (polyethylene 100% UV stabilized) to be used as synthetic grass        component.    -   Geotextiles/polyethylene and polypropylene fabrics.    -   The turf is ballasted with approximately about 0.5 to about 1.5        of sand infill. Placement of the sand will be done using air        pumps, spreader bars, etc., to deliver the material to the        slopes.

By way of general summary, but not in limitation, the present inventionprovides:

-   -   1. A synthetic grass turf that is combined with an impermeable        geomembrane on a soil supported base to form a final or a        temporary cover for landfills and other man made stockpiles    -   2. An impermeable geomembrane with a structurally self        supporting three-dimensional spacing device (studs) that, when        covered by the geotextiles of the synthetic grass, provides for        a drainage system without blocking the space between the studs        of the geomembrane.    -   3. A drainage system that will allow water to penetrate through        the sand and artificial grass layers into a transmissive zone        created by the studs, thus avoiding saturation and percolation        into the sand and wash off the surface of the cover system.    -   4. A drainage system wherein the surface water in the drainage        will be directed down the slope to drainage benches and down        chutes at certain lateral spacing as defined by the critical        length calculations described above. Surface water will then be        directed to the site perimeter ditches and surface water ponds.    -   5. A drainage system in which the spacing drainage can comprise,        instead of studs structured in the liner itself, a high-density        polyethylene drainage net that is applied directly on top of a        lower roughened-textured geomembrane liner to form a drainage        layer.    -   6. A drainage system that allows the installation of the        synthetic grass not only in relatively flat surfaces but also in        very steep slopes like those occurring in landfills and mine        stockpiles without eroding the sand off the cover system.    -   7. A method for providing a drainage system for a synthetic        grass turf on an impermeable geomembrane for the closure of        landfills by using a layering system that does not require the        use of heavy earthwork equipment. The method comprises the        steps:        -   a. Preparing the intermediate cover supported soil in flat            and slope areas;        -   b. Placing an impermeable membrane on top of the            intermediate soil cover used in landfills and stockpiles;        -   c. Placing the drainage system on top of the geomembrane.            This step can be avoided if a liner with studs drain liner            is used.        -   d. Laying the turf assembly on top the spacing device            drainage without performing any further preparation to the            drainage spacing; and        -   e. Placing about 0.5 to about 1.5 inch sand layer by blowing            and spreading the sand within the grass.    -   8. An infill layer of particulate material such as sand disposed        between the upstanding yarns of polyethylene grass of a depth of        less than the length of the ribbons and directly on top of the        geotextiles in which the ribbons are tufted.    -   9. A method that provides ballast to the cover system against        wind uplift created by high force winds on the mounding shape of        landfills and stockpiles. This eliminates the need of extensive        anchoring of the exposed geosynthetics.    -   10. A method that will provide for additional UV light        resistance to the one or more geotextiles in which the synthetic        polyethylene or polypropylene yarns are tufted.    -   11. A cover system for landfills and manmade stockpiles that can        be converted to Subtitle “D” covers and EPA regulated covers by        adding two feet of vegetative soil cover on top. The drainage        system and the sand layer will provide enough transmissivity to        comply with the government regulations for upper vegetated soil        infiltration drainage in environmental closures.    -   12. A cover system that provides high internal friction values        between the layers that will allow for the placement of two feet        of soil on sideslopes exceeding 3 horizontal:1 vertical at a        later date without sliding on the cover system.    -   13. A cover system for landfills in arid regions where grass or        other vegetation will not grow and obtaining “air quality        credits” for controlling fugitive dust emissions from wind        erosion.    -   14. For applications not requiring a transmissive layer, the        present invention can be used without the drainage component and        infill, and the synthetic grass applied directly on top of the        geomembrane.    -   15. A gas collection system for collecting and conducting the        landfill gas produced by a waste site to a burning flare,        offsite reuse or other destination.

This invention has been described with particular reference to certainembodiments, but variations and modifications can be made withoutdeparting from the spirit and scope of the invention.

1. A cover system for waste sites, wherein the cover system comprises:A. a synthetic grass which comprises a composite of at least onegeotextile tufted or knitted with at least one synthetic yarn and B. animpermeable geomembrane which is comprised of a polymeric material,wherein the cover system is used in the absence of a vegetative soilsupport top cover and wherein the textured geomembrane is used with asynthetic drainage component; and C. a system for the collection of gasproduced by the waste site, wherein the gas collection system comprisesone or more sections of a synthetic media system located under the coversystem and connected to one or more header pipes to remove the gas.
 2. Acover system as defined by claim 1 wherein the impermeable geomembraneis selected from the group consisting of high density polyethylene, verylow density polyethylene, linear low density polyethylene or polyvinylchloride.
 3. A cover system as defined by claim 2 wherein theimpermeable geomembrane is comprised of linear low density polyethylene.4. A cover system as defined by claim 2 wherein the impermeablegeomembrane is comprised of high density polyethylene.
 5. A cover systemfor waste sites, wherein the cover system comprises: A. a syntheticgrass which comprises a composite of one geotextile tufted or knittedwith one synthetic yarn; B. an impermeable geomembrane which iscomprised of a polymeric material; C. a drainage system comprising asynthetic drainage component, wherein the cover system is used in theabsence of a vegetative soil support top cover; and D. a system for thecollection of gas produced by the waste site, wherein the gas collectionsystem comprises one or more sections of a synthetic media systemlocated under the cover system and connected to one or more header pipesto remove the gas.
 6. A cover system as defined by claim 5 wherein theimpermeable geomembrane is selected from the group consisting of highdensity polyethylene, very low density polyethylene, linear low densitypolyethylene or polyvinyl chloride.
 7. A cover system as defined byclaim 5 wherein the impermeable geomembrane is comprised of linear lowdensity polyethylene.
 8. A cover system as defined by claim 5 whereinthe impermeable geomembrane is comprised of high density polyethylene.9. A cover system as defined by claim 1 wherein the impermeablegeomembrane is textured.
 10. A cover system as defined by claim 5wherein the impermeable geomembrane is textured.